Pollinator diversity and crop pollination services are at risk.

In a recent opinion article in TREE, Ghazoul [1] questions the existence of a global pollinator crisis and, in doing so, raises some important points about the uncertainty of human dependence upon pollination services. We agree with Ghazoul [1] that much uncertainty remains regarding pollinator–pollination declines. However, we think that his assessment draws biased conclusions for pollinator declines from existing studies, misrepresents the extent of agricultural reliance on animal pollination, and underestimates the extent of pollination reduction in intensive monocultures. In his article [1], Ghazoul suggests that a pollinator crisis is driven mainly by reported declines of honeybees in North America, and bumblebees and butterflies in Europe. However, local and regional declines of solitary wild bees, bumblebees and honeybees owing to habitat loss, agricultural intensification and pesticide use have been reported in both Europe and America [2–5], and the impact of habitat loss, measured by species–area relationships, is much stronger for native bees than for other insect groups [6]. For genetic reasons alone, bees are more extinction prone than are other taxa, because single-locus sex determination makes them particularly sensitive to the effects of small population size through the production of sterile diploid males [7]. Pollinators, other than honeybees and bumblebees, have many Red Data Book entries (e.g. for 11 European countries, an average of 27.4% of the national bee fauna is listed) because they are known to be threatened or declining. Thus, there is convincing evidence for negative impacts of habitat loss and agricultural intensification on pollinator diversity for a range of taxa across continents, although some species might profit regionally from climate warming [1]. Ghazoul assumes that a few remaining generalist pollinators will ensure pollination services in the future [1]; however, even crops with generalized pollination